Abstract A45: Investigating the role of ASCL1 in regulating differentiation of gliobastoma precursor cells

Abstract

Abstract Glioblastoma (GBM), the most common and lethal adult primary brain tumour, exhibits cellular heterogeneity and a subpopulation of tumour cells exhibits the neural precursor phenotype and drives tumourigenesis. These findings suggest that tumours may represent aberrant organogenesis with growth caused by unlimited proliferation and failure of differentiation of malignant precursor cells. It has yet to be determined the relative importance of aberrant self-renewal versus blocked differentiation in the brain tumour phenotype. As GBM-initiating cells have precursor cell properties, promotion of differentiation represents a potential strategy for treatment. Forcing glioblastoma precursor cells (GPCs) to differentiate terminally would limit clonal expansion and attenuate tumour growth. Data generated in our lab suggests that differentiation potential varies between different patient-derived GPC cultures. This study aims to determine what defines a blocked differentiation phenotype in human glioblastoma and to determine whether differentiation therapy is a feasible strategy for glioblastoma treatment. A key regulator of neuronal differentiation is ASCL1 during normal development and adult neurogenesis. Microarray analysis of ASCL1 expression in GPCs (n = 33) revealed two subgroups of GPCs as having either high or low expression. Preliminary evidence suggests that GPCs with high expression of ASCL1 exhibit neuronal lineage commitment whereas GPCs with low expression of ASCL1 do not undergo lineage commitment. This was confirmed using immunocytochemistry, quantitative real-time PCR and Western blot analysis. Furthermore, an inverse correlation was observed between transcript levels of ASCL1 and DKK1, an antagonist of the Wnt signalling pathway, while a direct correlation was observed between ASCL1 and activated β-catenin (ABC). Treatment of GPCs with a GSK3β inhibitor resulted in the activation of Wnt signalling and concomitant increase in transcript levels of ASCL1 and neuronal lineage markers (i.e. TUJ1, MAP2). This study aims to further investigate the role of ASCL1 in glioblastoma and to determine whether neuronal lineage commitment in the context of ASCL1 activity is mediated in a Wnt-dependent manner. Gain- and loss-of-function studies are in progress to determine whether ASCL1 is sufficient and/or necessary for neuronal lineage commitment and consequent effects on tumour-initiating properties (i.e. proliferation and self-renewal) will be examined in vitro and in vivo. Citation Format: Nicole I. Park, Peter B. Dirks. Investigating the role of ASCL1 in regulating differentiation of gliobastoma precursor cells. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr A45.